Many corticosteroids are known having heterocyclic rings fused in the 16- and 17-positions. U.S. Pat. No. 3,048,581, issued Aug. 7, 1962, discloses the preparation of acetals and ketals of 16,17-dihydroxypregnenes. U.S. Pat. No. 3,349,084, issued Oct. 24, 1967, discloses the preparation of steroidal [16,17-d]-2'-isoxazolines. These are, of course, only exemplary of the known steroids having a heterocyclic group fused in the 16,17-position.
The reaction of isonitriles containing an .alpha.-hydrogen atom with .alpha.,.beta.-unsaturated carbonyl compounds in the presence of catalytic amounts of cuprous oxide is known; see, for example, Saegusa et al., J. Org. Chem., 36, 3316 (1971). It is also known that the reaction can be catalyzed by bases such as sodium ethoxide. The use of these reactions in the field of steroid chemistry has resulted in the preparation of novel steroidal [16.alpha.,17-c] [2H]pyrroles.